1. Field of the Ivention
This invention relates to stabilized screen printing.
2. Description of the Prior Art
Many types of screen printing apparatus are known but many suffer difficulties with accuracy of alignment and indexing and in structural complexity and cost. Applicant has been active in the design of screen printing apparatus and reference is made to U.S. Pat. Nos. 5,189,950; 5,031,527; 4,974,507; 4,962,702; and 4,934,263 all of which disclose effective and useful apparatus. Reference is now made to drawings illustrating certain prior art apparatus.
Reference is made to FIG. 1A which shows a base 1, a central column 2 secured to the base, a rotor 3 which rotates on the column 2 between a number of radially indexed positions and which carries part 4 of screen printing apparatus. The rotor 3 has a bearing (not shown) which is mounted to rotate on the column 2. A stator 6 is mounted for vertical movement on the column 2 and has a bearing (not shown) which can move on the column 2 to guide the stator in vertical position from the full line position to the dash line position as shown. The stator 6 carries part 7 of screen printing apparatus. Cost and accuracy problems associated with the above machine are that the column 2 needs to be massive and must be machined over a substantial length to provide accurate bearing surfaces for the bearing associated with the rotor 3 and the bearing associated with the stator 6.
Reference is made to FIG. 1B which shows a base 21, a central column 22 secured to the base, a rotor 23 which rotates on the column 22 between a number of radially indexed positions and which carries part 24 of screen printing apparatus. The rotor 23 has a bearing (not shown) which is mounted to rotate on the column 22. A stator 26 is mounted on the column 22 and carries part 27 of screen printing apparatus which is pivotably mounted to the stator 26 to move between the full line position to the dash line position as shown. Cost and accuracy problems associated with the above machine are that the column 22 needs to be substantial and must be machined to provide accurate bearing surfaces for the bearing associated with the rotor 23.
Reference is now made to FIG. 1C which is similar to the apparatus shown in FIG. 1B and like numerals denote like parts. In this case, however, part 37 of screen printing apparatus is carried by towers 38 to move between the full line position and dash line position as shown. The machine shown in FIG. 1C has similar cost and accuracy problems to the machine shown in FIG. 1B.
Reference is now made to FIG. 1D which shows a base 41, a central column 42 secured to the base, a rotor 43 which rotates on the column 42 between a number of radially indexed positions and which carries a part 44 of screen printing apparatus. The rotor 43 has a bearing comprising upper and lower parts 45 and 49 which is mounted to rotate on the column 42. A stator 46 is mounted to the column 42 and carries part 47 of the screen printing apparatus. In use the rotor 43 can be raised from the full line position to the dash line position as shown with the bearing parts 45 and 49 guiding. Cost and accuracy problems are similar to those in respect of the machine shown in FIG. 1A.
Reference is now made to FIG. 1E which shows a machine similar to that shown in FIG. 1D and like numerals denote like parts. However, in this instance lifting cylinders 51 are located a substantial distance from the column 42. Cost and accuracy problems are similar to those discussed in respect to the machine shown in FIG. 1A. Other difficulties associated with some of the above machines are that lifting loads are too close to the column and there is a lack of registration accuracy.